Syringes are known for storing and transporting substances with fluid properties such as gases, liquids, pastes, slurries, and the like. A syringe may include a barrel defining a bore in communication with a port, and a piston disposed within the barrel. Translation of the piston away from the port may draw material into the barrel through the port. Alternatively, translation of the piston toward the port may expel material out of the barrel through the port.
A syringe barrel may be formed from a transparent or translucent material, such that a position of the piston within the bore is visible through the barrel. Further, the syringe barrel may include indicia disposed thereon, such that longitudinal alignment of the piston relative to the indicia may visually indicate a volume of material stored between the piston and the port.
U.S. Pat. No. 5,009,645 (hereinafter, “the '645 patent”) purports to describe a syringe for dispensing measured quantities of a material (e.g., a medicament). The syringe from the '645 patent includes a barrel, a plunger rod having a cruciform transverse cross section, and an infinitely adjustable stop member secured to the plunger rod for positively setting the length of travel of the plunger rod to thereby control the volume of material dispensed from the syringe. However, sequential delivery of multiple doses using the syringe from the '645 patent may be subject to dosage errors resulting from inaccurate displacement of the infinitely adjustable stop member between dose deliveries, undue time consumption to adjust the position of the infinitely adjustable stop member, or both.
U.S. Patent Publication No. 2005/0137532 (hereinafter, “the '532 publication”) purports to describe a unit to administer medication having a plunger with non-reusable stroke stops sequentially arranged along the plunger. According to the '193 patent, the stroke stops are frangible about a weakening line, such that each broken stroke stop enables the forward movement of the impelling plunger and the administration of a corresponding dose. However, the stroke stops of the '532 publication may interfere with filling an empty syringe so configured, and therefore limit application to pre-filled syringes. Further, the stroke stops of the '532 patent are inherently non-reusable because of their frangible nature, and the stroke stops may be complex and expensive to manufacture.
U.S. Pat. No. 5,318,544 (hereinafter, “the '544 patent”) purports to describe a syringe for metering predetermined volumes of fluid therefrom. The syringe of the '544 patent includes a tube, a clip, and a metering plunger having stop surfaces disposed thereon, where the plunger is inserted through an opening in the clip and is slidably located within the syringe tube. However, the plunger stop surfaces of the '544 patent have complex shapes that could be difficult or expensive to manufacture. Further, the stop surfaces of the '544 patent may interfere with filling an empty syringe by requiring rotation of the plunger in addition to axial translation during a filling step.
U.S. Pat. No. 6,579,269 (hereinafter, “the '269 patent”) purports to describe a syringe with a structure that allows variation in sliding displacement of the plunger which may be accompanied by an audible sound. U.S. Patent Application Publication No. 2009/0287161 (hereinafter, “the '161 publication”) purports to describe a syringe including physical stops or dosage administered indicators which can act to prevent hydraulic momentum from continuing to deliver fluid after thumb pressure is lifted off of the push rod. However, neither the '269 patent nor the '161 publication provides asymmetric ramps for tailoring differences in deceleration and acceleration resistance forces for movement of a plunger within a dose dividing syringe.
Accordingly, there is a need for apparatus and methods to address the above-identified shortcomings of conventional syringes, as well as other shortcomings in the art.